Los Angeles Galaxy head coach Bruce Arena might have taken the words out of everyone’s mouths when he said that the 2010 conference semifinals were “the craziest thing I’ve ever seen.”

Certainly, the four teams left should be prepared for anything, and if the MLS Cup Playoffs have not done enough to convince the conference championship hosts to be on upset alert, history will.

MLSsoccer.com takes a look back the league’s long history of upsets in the second round of the playoffs.

1996 – The Tampa Bay Mutiny ran away with the Supporters’ Shield in Major League Soccer’s inaugural season. Their 58 points to end the regular season were nine more than the second-place Los Angeles. The Mutiny stormed past the Columbus Crew in the Eastern Conference semifinal by a combined score of 7-3.

But then the Eastern leaders ran into D.C. United and were unceremoniously eliminated in two games. United went on to win the MLS Cup.

1997 – In the MLS Cup Playoff’s second edition, the Colorado Rapids earned the somewhat dubious distinction of becoming the first team in league history to make the MLS Cup Final despite a losing record in the regular season.

Their less-fortunate opponents in the Western Conference Championship? The Dallas Burn, who went 16-16 in 1997 and eliminated the ’96 finalist Galaxy before falling to the Rapids.

1998 – It’s sometimes forgotten how surreal the Chicago Fire’s run to MLS Cup glory was in 1998. Not only were they the first – and to this day, only – expansion team to open with a title, they were also the first team not named D.C. United to win it all.

En route to the MLS Cup, the Fire burned up Supporters’ Shield-winning LA Galaxy in the conference final.

Miami got off to a good start by winning the Supporters’ Shield, but were then toppled in overtime by the No. 5 seed San Jose Earthquakes one round before the Final.

On the other side of the bracket, the Fire played three straight overtime games against the Galaxy in a first-to-five-points series. Eventually, LA won the series, winning two and tying one. It’s hard to even count this as an upset, but the Galaxy were the third seed while the Fire were second.

2005 – The Galaxy were the underdogs against the Rapids? Seems strange to say it now, but both teams had compiled a 13-13-6 record in 2005, with Colorado edging LA on goal differential.

Almost poetically, the match turned out to be a bit of a nail-biter. After scoring in the 28th minute, the Galaxy surrendered nine shots before Landon Donovan finally doubled the difference in the 88th.

LA went on to beat New England in the final.

2006 – D.C. United edged out the New England Revolution for the regular season Eastern Conference lead by seven points. But he who laughs last laughs the loudest, and the Revs won the conference championship 1-0 at RFK Stadium.

2008 – In one of the most bizarre playoff runs in MLS history, the New York Red Bulls made the dance on the last day of the season by virtue of a D.C. United loss to the Columbus Crew.

New York then went on to win the Western Conference by beating Real Salt Lake 1-0 at Rio Tinto Stadium. That result remains RSL’s only playoff loss at home.

2009 – After their loss to New York, RSL tried a similar technique by just barely squeezing into the playoffs.

As the bottom seed, the Claret-and-Cobalt stunned MLS by beating the blue-blooded, Eastern Conference second-seeded Chicago Fire on penalties.